Using Mulches in the Landscape

Every gardener knows that mulch is beneficial for their trees, shrubs and ornamental plantings, right? But how accurate is your knowledge of mulch? Test yourself by answering the following true or false questions.

Mulch is applied in the fall to keep the plant and the underlying ground warm.

Plants that die during the winter are killed by cold temperatures.

A one-inch layer of mulch is adequate for winter protection of most plants.

Question #1

The answer to question #1 is false. Mulch is applied in late fall to moderate soil temperatures, and prevent soil temperature fluctuations during the winter. Plants can better tolerate soil that is continually cold or frozen, than soil that fluctuates up and down throughout the winter.

If mulch is applied too soon in late summer, when soil temperatures are still warm, it can keep the underlying soil warm and delay the hardening-off process in landscape plants. This makes them more susceptible to damage from early winter freezing temperatures.

Mulch should not be applied in fall until the ground has cooled. Wait until after several hard freezes with temperatures dipping into the 20's. All trees, shrubs and perennials planted this summer, or divided in fall, would benefit from an application of winter mulch.

A layer of mulch about three inches thick is best. Good organic mulches include wood or bark chips, shredded bark, pine straw, evergreen boughs, clean straw or ground corncobs. Ideally mulch should not compact too easily. Tightly compacted mulch can obstruct water and air movement in the soil, which often happens when green grass clippings are used, and may result in poor water drainage and increased disease development, such as crown or root rots.

Question #2

The answer to question #2 is false. Newly planted trees, shrubs and perennials damaged or killed during winter usually are not injured directly by cold temperatures, but indirectly by frost heaving or desiccation. Frost heaving occurs when the soil alternately freezes and thaws, resulting in damage to the dormant crown and root system. Frost heaving is reduced in plantings where an application of winter mulch is made, through its ability to reduce swings in soil temperatures.

Winter desiccation is a common type of winter injury that occurs when the amount of water lost by the foliage exceeds the amount picked up by the roots. Mulch holds moisture in the soil, minimizing the effects of dry winter conditions.

Question #3

The answer to question #3 is false. Winter mulch should be applied at a depth of 3-4 inches. With fine organic mulches, such as compost or shredded leaves, maintain a 3-inch layer. For coarse materials, like wood chips, maintain a 4-inch layer. Remember a 4-inch layer will compact to 3 inches.

Don't exceed this recommended thickness, or pile mulch up around the base of trees. Excessively deep mulch provides excellently protected habitat for voles, which may eat the bark off your young trees in winter, and will hold moisture against the bark of your tree which could lead to bark death.

In time, excess mulch often results in root growth into the mulch layer. Plants rooted in the mulch layer are more likely to experience winter and drought injury than those growing in soil, due to the poor water holding capacity of loose, non-compacted mulch.

This resource was updated October 2013 and appeared in the Lincoln Journal Star Newspaper Sunday edition. For information on reproducing this article or using any photographs or graphics, read the Terms of Use statement

PHOTO Credit: Vicki Jedlicka, UNL Extension in Lancaster County

University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office